The Emacs Lisp language
The built-in help system in Emacs provides on-the-fly help pages on functions (C-h f), variables (C-h v), and other Emacs Lisp concepts. See C-h C-h for an overview of the help system.

Examples
Perhaps the best way to make your Emacs working environment more efficient is to borrow ideas and code from other users. A web search for “dot emacs” or “my emacs” returns many examples. Here are links to mine: